Reproducer



Feb 21, 1933. I W q; GRUNQW 1 898A41 REPRODUGER Filed June 8, 1928 2 Sheets-Sheet l Feb. 21, 1933. w Q GRUNQW 1,898,441 I REPRODUGER Filed June 8, 1928 2 Sheets-Sheet 2 ZGD WW a 34%. 21 Ji /eman- MG. Gmuww Patented Feb. 21, 1933 UNITED STATES PATENT OFFICE WILLIAM C. GR'U'NOW, OF CHICAGO, ILLINOIS, ASSIGNOR TO GRIGSBY-GRUNOW COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION .OF ILLINOIS REPRODUCER Application filed June 8 1928. Serial 110. 283,762.

My invention relates to electromagnetic sound reproducers and more particularly to an electromagnetic sound reproducer which employs a free edge sound reproducing .dia-

6 phragm having an exciting coil secured thereto. I

In this type of reproducer a direct current electromagnet is provided, having a central core and an outside casing brought together in such a way as to leave a circular air gap across which exists an intense magnetic field. A freelysupported cone disposed adjacent the direct current coil has a moving or exciting coil secured at its apex and disposed in 1. the circular direct current field. It is high 1y important that this moving coil 'be accurately positioned in order to secure the best results. It it furthermore-desirable to employ a cone which will at all times have .20 .the same physical characteristics, independent of the influence of the weather, etc.

Accordingly one of the principal objects of my invention is the provision of an improved electromagnetic sound reproducer 2 having the desirable characteristics suggest- Another object is to provide means for centering the coil accuratelyin the magnetic field. 1

Another object is to secure the coil ,to the cone in such a way that-its axis will be dead in line with the axis of the cone.

Another object is to provide improved means for attaching the movable coil to the .35 apex of the cone.

. Another object is to employ the direct current electromagnet core as a support for the cone without diminishing the magnetic field in the circular gap.

Another object is the provision of a cone which will be unaifected by weather conditions. v

Other objects and features of the invention willbe apparent from a consideration of the detailed description taken with the accompanying drawings, wherein Fig. 1 is a vertical central section through a reproducer of our invention, a portion of the figure being shown in elevation;

Fig. 2 is a fragmentary elevational view looking at the front of the cone;

Fig. 3 is an enlarged central sectional view showing the manner in which the cone and moving coil are secured; and

Fig. 4 is an enlarged perspective view of a reinforcing ring employed for securing the coil to the cone. 1

In the form of my invention shown in the accompanying drawings certain novel fea- (so tures are combined, resulting in a reproducer which as a whole is considerable of an improvement over similar reproducers with which I am familiar. Some of the features of the invention, however, may be incorporated with reproducers of different types and the entire structure may be modified without departing from the spirit and scope of the present invention.

The reproducer comprises a base 10 sup porting a casing 11 housing a direct current coil 12 and having end plates 13 and 14: held together by bolts 16. A core 17 has a narrowed shank 18 extending through one end plate 14, to which shank a nut 19 is threaded, thereby securing the core in position. The end plate 13 is provided with a circular openi11g13a into which the end of the core 17 projects, as shown with particu- I lar clearness in Fig. 3. The casing 11 with its end plates and the core 17 form the poles of a direct current electromagnet and as a Consequence the annular gap between the unsupported end .of the .core and the associated portion of the plate 13 has a very heavy magnetic field. As it is desirable that the center. pole piece be positioned very accurately with respect to the outer pole piece, a spacer plate 21 of non-magnetic material is secured to the end plate 13 and is apertured to receive the core 17, thematerial of the supporting plate being bent out of its regular plane at 210 to provide ample space for the movement of the floating coil.

In the type of reproducer herein pictured, the actuating orinoving coil is secured .to the apex of the cone andtheentire cone being freely suspended moves as a body. It is in the construction of the cone and securing the coil thereto, together with an improved selection of materials, which are principally responsible for the improved characteristics of our speaker.

I provide a cone 22 which cannot be affected by changes in temperature, humidity, or the like. "The particular material which ll employ is that known as latex pa per, wherein rubber in colloidal form is incorporated with the paper pulp before its conv rsion into paper. The colloidal rubber may be either the natural latex or an artificial latex, the only requirement being that the rubber be dispersed throughou the paper in minute divisions. The finished paper is unpolished and on casual inspection appears to have the texture of ordinary blotting paper, but the incorporation of the rubber therewith prevents the absorption of moisture and a cone formed such paper will maintain its physical characteristics, as far as l know, indefinitely.

The cone is preferably secured both at its base and apex. Accordingly, on the outside or bell portion of the cone a rubberized cotton strip i secured, preferably by the employment of suitable adhesive This has secured to the outside thereof a ring 24 of suitable material, as for example cardboard, and the outside of the cloth 28 and cardboard ring are clamped between a plurality of clamping members 26 and the flared outside edge of a supporting frame 27 secured to the plate 13 by the bolts 16. The frame 27 is in the form of a casing but is provided with apertures 27a, serving a variety of useful purposes. lhe rubberized cloth 23 which 1 employ with the best results is that known as bellows stock and consisting of a relatively fine grade of sheeting covered on one side witl a thin coating of rubber.

The floating coil 28 is secured on a hollow paper core 29 of cylindrical conformation and having the truncated edge 31 of the cone 22 serrated and adhesively secured to the outside surface of the cylindrical core 29. A thin metal insert 32, preferably of very thin aluminum, is provided with a cylindrical portion 320: which extends on the inside of the paper core 29, the contacting surfaces eing secured together by suitable adhesive; an outwardly extending portion 326 at right angles to the cylindrical portion 32a and serving as a stop for the cylindrical core 29; and an out-flaring portion 320 secured to the inside of the cone 22. The out-flared portion 320 is provided with apertures 32d which facilitate the securing of this portion of the insert to the cone,'the adhesive being permitted to extend partly into the apertures 32d, and the material struck from the apertures extending slightly into the material of the cone so as to obtain a species of mechanical connection as well.

With this construction I am able to align the axes of the coil 28 and the cone 22 Very accurately so that there is very little difficulty in adjusting the coil 28 to a position concentric with the magnetic gap between the pole pieces. Not only is the alignment more easily obtained by this construction, but there is small likelihood of the coil be coming detached from the cone through constant use or by being subjected to rough handling.

he inner or apex end of the cone is secured to the center pole piece 17. T o accomplish this a non-magnetic insert 33 is driven into the apertured end of the pole piece so as to become a continuation thereof. A. transverse supporting member 84 is disposed across the inside of the cone immediately adjacent the metal insert 32 and has an out- I flaring flange 3% of annular character, which is adhesively secured to the inside of the cone as illustrated with. particular clearncss in Fig. The central portion of this member is apertured to receive the shank of a machine screw 36 and the end of the pole piece extension is hollowed out so that the member is gripped tightly between the head of the screw and the end face of the pole extension. This clamping arrangement permits the cone to be moved around slightly when placed in position and when once the screw 36 is driven down tightly, the position of the apex end of the cone and the coil 28 will remain unchanged. The supporting member 8 lis provided with apertures 34m and 34b to facilitate the movement of the cone, as all bodily movement of the cone must result in a flexing of the member The ends of the coil 28 are brought out to conductor leads 37, as shown in Fig. 1, and these leads extend to a small mounting panel 38 secured within the base 10. The leads (not shown) from the coil 12 are also extended downwardly into the base 10 for connection to suitable terminals carried by the panel 38. Accordingly, connections to the speaker are made entirely to suitable terminals supported by said panel.

By making the pole piece extension 33 of non-magnetic material the magnetic lines across the circular gap between the pole pieces will be increased and at the same time the pole piece or core 17 be used as a fixed support for the supporting piece 34 of the cone. This supporting piece may be made of any suitable material, but apparently the best results are obtained with thin, durable fibre stock.

As previously suggested, the features of my invention are particularly adapted for use with a speaker of the class described and shown, but I do not restrict myself to the combination of these features in any particular form and the invention is limited only by the scope of the appended claims.

What I claim as new and desire to secure by United States Letters Patent is 1. In a reproducer of the character described, a vibratory truncated cone, a cylindrical core secured to the cone having a moving coil wound thereon, and an insert disposed on the inside of the cone and on the inside of the cylindrical core for reinforcing the connection between the same.

2. In a reproducer of the character described, a vibratory truncated cone, a cylindrical coil supporting core having one end disposed within the truncated edge of the cone, and a reinforcing metal insert disposed on the inside of the cone and cylindrical coil supporting core.

3. In a reproducer 0f the character described, a vibratory cone having a serrated truncated edge, a cylindrical coil supporting core disposed within the cone with the serrated edge of the cone adhesively secured to the outside of said core, and a reinforcing insert disposed on the inside of the cone and Core.

4. The combination described in claim 3, wherein said insert has a stop against which the core rests to predetermine its position with respect to the cone.

5. The combination described in claim 3 wherein the insert has an outwardly extending flange for determining the position of the cylindrical core, and an outflared portion lying along the inside outwardly extending surface of the cone. 7

6. An insert for reinforcing reproducer cones of the character described, consisting of a cylindrical portion, a portion at right angles to the cylindrical portion, and a portion outflared from the right angle portion.

In witness whereof, I hereunto subscribe my name this 1st day of June, 1928.

WILLIAM G. GRUNOW. 

